I just came across this thread and thought I'd put in my 2 cents. As already stated in this thread, the reason there is a withdrawal time with ivermectin is because it can be found in the eggs (specifically the yolks) of treated hens. The amount is to small to hurt anyone, and within a small backyard flock is unlikely to contribute greatly to parasite resistance. However, remember that we, even as small backyard owners, are part of the animal agriculture sector. Animal agriculture is getting a lot of hate these days, and some of that hate is coming from people who are concerned about drug resistance. I have zero problem with the use of antibiotics or any drugs within animal agriculture, I use them and I advocate for it. I believe it offers our animals a better quality of life and in most areas it is used with great caution and responsibility. That being said, I think we should all try to follow guidelines as best we can, so that we all can be as effective "agvocates" as possible. Just my perspective.